Pardon my naivete, but how does this work??

First, you are right to be suspicious. It is quite likely that many of those tickets are fake or non-existent.

But, the point of that "general public" disclaimer is that special blocks of tickets are sold earlier to special agencies and partners of the concert/venue organizers.

Lastly, they avoid the laws either by special exception, which is not hard to get if you have the right lawyers to swim thru the paperwork, or by basing their company outside the jurisdiction, say ... Sweden or someplace.

Many times when a concert/event is scheduled in a large arena, before the tickets are even printed there is an agreement with the ticket agencies that a percentage of the tickets will be for them. I can't say this is true for all arena's but here in Kansas City it is a proven fact.

The ticket agencies like Ticketmaster and Chub Hub can get around the scalping by saying these are processing fees or printing fees or something like that.

One way they get away with it here is scalping is not illegal. I do believe it should be but the laws govern them and they take advantage of it.

One way to get away with selling tickets over face value is to sell something with a ticket.

For example, if the ticket is $100 and your selling it for $200 with a keychain, you can argue that the ticket is $100 and the other $100 is the keychain,

Most of them buy large lots of tickets the day the actual tickets go on sale to cover what they have sold online. As far as anti scalping laws go. Report them, you wont get any traction on the issue, but report them anyway.